On Thu, 17 Feb 2000, Matthew Raney went:
> I had a student ask what the effects of significantly high levels of
> serotonin might be, and wasn't quite sure.
I think the best answer is another question: "High levels of serotonin
_in what place_, affecting _which receptors_?" It's usually not
informative to make global statements about "levels of serotonin"
(although neuroscientists do it anyway). Serotonin in the brain may
increase or decrease anxiety, may impair or facilitate memory
consolidation, may reduce nausea or induce vomiting. Serotonin acting
on blood vessels causes vasoconstriction. See, we're talking about a
neurotransmitter that can activate any of 14 different kinds of
receptors (some of which have opposing functions) found all over the
brain and the rest of the body.
So the question is kinda like "What are the effects of significantly
high levels of money?" It depends where it's spent.
If you take a high dose of a drug that globally increases levels of
serotonin in synapses (Prozac would be one example), you can get
"serotonin syndrome": confusion, agitation, fever, shivering,
sweating, diarrhea, and myoclonus (muscle twitches). This is thought
to be due mostly to hyperactivation of one subtype of serotonin
receptor (the 5-HT1A receptor), especially in the brainstem and spinal
cord (though some of the action is presumably taking place in other
brain regions and in the digestive tract, which has serotonin
receptors of its own). So "serotonin syndrome" is what you would
notice if you artificially jacked up your "serotonin levels" beyond
what's physiologically normal.
And similarly, on Thu, 17 Feb 2000, Jean Edwards went:
> ... My general understanding of ACh is that when production
> of this neurotransmitter is blocked or receptors are prevented from
> receiving it, then, in the worse case scenario, paralysis could
> occur ( as in curare). Over production of ACh, I've read is
> associated with muscle contractions, spasms, etc.
Right; that's what ACh does _on muscle cells_.
> However, while reading an article on sleep and dreams in the Annual
> Editions of Psychology (00/01), the author states that during sleep,
> the brain is "soaked in acetylcholine, which seems to stimulate
> nerve cells while it strips muscles of tone and tension (pg 52)."
Here the author is talking about what ACh does _in the brain_. So
there's no contradiction (though the language seems a little sloppy).
I'm guessing that the author was referring specifically to REM sleep,
when ACh is released in rhythmic bursts from the brainstem into part
of the thalamus.
> The author also adds that serotonin levels plummet.
During REM sleep, serotonin release into various brain regions is
indeed lower than in non-REM sleep or quiet waking.
Disclaimer: I'm not too well-read in the physiology of sleep.
--David Epstein
[EMAIL PROTECTED]
